If your home is or can be wire-networked, you can build a Home Theater PC (HTPC) with a multi-tuner card attached/added. This multi-tuner device would require a cablecard from your cable company, but it would support up six simultaneous channels (more if you have multiple multi-tuner cards). In addition to the HTPC, each TV location would require a media extender device which could be assigned one of the tuners from the multi-tuner card.
There is a high, upfront cost here, but, depending on how many set top boxes you currently need (and can get rid of), eventually there will be a cost savings.
-Wolf sends